This invention relates to an optical pickup using a waveguide and in particular to a solid state optical pickup suitable for an optical information recording/reproducing device using optical discs, optical cards, etc. as recording medium.
In a prior art optically integrated optical pickup, elements having functions of light collection, coupling, splitting and light detection are integrated in a waveguide layer, which is a plane single layer, as disclosed in the Journal of the Electronic Communication Society of Japan Optical Quantum Electronic Study Group (OQE) 85-72. In this device a semiconductor laser diode is mounted on an end surface of an optical waveguide so that light emitted by the semiconductor laser diode propagates in an optical waveguide layer and is collected by a focusing grating coupler so as to form a fine light spot on an optical disc, which is recording medium. Light reflected by the optical disc is returned again to the focusing grating coupler and led to the optical waveguide layer. This returned light is splitted and collected by a twin grating focusing beam splitter and propagates in the optical waveguide layer towards 4 photodiodes.
By the prior art construction described above, since both the light going to the optical disc and the light returning therefrom propagate in the optical waveguide path, both the lights must pass through the twin grating focusing beam splitter for leading the returning light to photodetectors. Consequently there is a problem that the light detection efficiency is remarkably reduced.